Astronomers have noticed something really strange about the data from the Gaia space observatory. The distant star oddly cleared, then faded. A few weeks later, it brightened again and faded again.
This strange behavior was not caused by the processes produced by the star; rather, the gravity of the invisible object between us was curving the fabric of spacetime, amplifying the light of the star.
Now astronomers have figured out what this invisible object is: a double star located at a distance of 2.544 light years, so dim that it practically does not emit light. However, based on how the star's gravity increases its luminosity, astronomers were able to calculate its mass, distance, and orbit.
These methods, they said, could be used to detect other hidden massive objects in the Milky Way galaxy, such as millions of lonely black holes of stellar mass.
According to a group of astronomers, the key to understanding the nature of the system was that the original object was constantly brightening and darkening. The event was named Gaia16aye.
“If you have a single lens caused by a single object, there will be a small, steady rise in brightness, and then there will be a gradual decrease as the lens passes in front of the source and then goes away,” said astronomer Lukasz Wyrzykowski of the University of Warsaw in Poland.
'In this case, the brightness of the star not only dropped sharply, but after a couple of weeks it became brighter again, which is very unusual. Over the course of 500 days of observation, we saw it change brightness five times. '
This assumes a binary object producing a so-called gravitational microlens; an effect predicted by Einstein that occurs when the gravity of a foreground object causes spacetime to bend, magnifying something behind it.
On a large scale, this allows us to study distant objects, but smaller lenses can also be useful.
In the case of Gaia16aye, the microlenses were a complex network of high magnification areas. The background sources transmitted by these regions quickly clear up and then dim again as you move.
A careful study of these patterns in the Gaia16aye microlensing event revealed a binary star system called 2MASS19400112 + 3007533, two red dwarf stars with a clock rate of 57% and 36% of the Sun's mass. They revolve around a common center of gravity every 2.88 Earth years.
“We don’t see this binary system at all, it was only by seeing the effects it created by acting as the lens of the background star that we were able to talk about it,” said astronomer Przemek Mruz, a former university employee. Warsaw and now at the California Institute of Technology.
“We could determine the period of rotation of the system, the masses of its components, their separation, the shape of their orbits – basically everything – without seeing the light of the binary components.”
The team hopes these methods will help them find stellar mass black holes – one of the goals of an automated tool to find bright and darkening stars in Gaia data.
At the moment, we know of several dozen of these black holes. We notice them when they interact with things in space around them, such as when they 'bite' at a star, or when they are binary paired with a normal star.
Today, however, dormant black holes remain elusive. But if we can find invisible red dwarf stars that collectively are less than the mass of the Sun, these methods could reveal black holes of stellar mass, which, as is customary, have a lower limit of about five times the mass of the Sun.
“Our method allows us to see the invisible,” Wyrzykowski said.
The study was published in Astronomy and Astrophysics.
Sources: Photo: Maciej Rębisz
